Security camera footage, shell casings and a small but distinctive tattoo played pivotal roles in the arrest of a man suspected in at least six killings over the past two months in the St. Louis and Kansas City areas.

The St. Louis Circuit Attorney's office on Tuesday charged Perez Deshay Reed in the shooting deaths of two people in the city in September.

Reed was charged Saturday in two other fatal shootings in September in St. Louis County.

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He is also suspected of killing two people in Kansas City, Kansas, and the FBI has labelled him a suspected serial killer.

Reed, who turns 26 years old Wednesday, remained jailed on a $2.7 million bond Tuesday and didn't yet have an attorney.

Surveillance video in Kansas helped lead to Reed's arrest.

Images captured by the cameras showed the distinctive crescent moon-shaped tattoo on Reed's forehead.

Another key factor was evidence left behind at each of the St Louis-area shootings.

“The commonality among them were handgun casings,” Rich Quinn, special agent in charge of the FBI office in St Louis, said.

“We knew they came from the same handgun.”

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Reed is charged in the St Louis County killings of 16-year-old Marnay Haynes on September 13 and 40-year-old Lester Robinson on September 26.

In the city of St Louis, he is suspected in the killings of 49-year-old Pamela Abercrombie on September 16 and a 24-year-old man, Carey Ross, on September 19.

All four victims were shot in the head.

His capture followed the killing of a man and a woman at a Kansas City, Kansas, apartment complex.

Surveillance video showed Reed entering Damon Irvin's apartment on October 28.

Police found Irvin, 35, fatally shot in the apartment on November 1, according to an FBI affidavit.

Reed and 25-year-old Rau'Daja Fairrow entered the same apartment complex on the night of October 29 and Reed left 15 minutes later, according to the affidavit.

Fairrow's nude body was found on November 2 in her apartment.

The FBI said Reed showed his driver's license to enter the building, and the surveillance video showed his forehead tattoo.

Officers began tailing Reed and were watching Friday as he boarded a St. Louis-bound Amtrak train that left Union Station in Kansas City, Missouri.

But instead of riding to St. Louis, Reed got off at the first stop in the Kansas City suburb of Independence, Missouri, the FBI said.

Officers conducting surveillance from aboard the train arrested Reed as he boarded a bus.

He was allegedly carrying a .40-calibre handgun that investigators believe he used in the St. Louis-area shootings.

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During an interview with police, Reed denied that he hurt anyone, according to the affidavit.

Investigators haven’t ruled out the possibility that Reed committed additional crimes.

St. Louis County Lt. Craig Longworth said there was no known connection between the victims.

“These seemed to be random acts,” he said.

Reed has connections to the St. Louis and Kansas City areas.

He began living with a cousin in St. Louis County in 2004 when he was eight years old, and she later became his legal guardian when his parents were deemed “unwilling, unable and unfit” to care for him, the St. Louis Post-Dispatch reported.

He was charged with misdemeanour assault in St. Louis County in 2019, though that case hasn't gone to trial.

He had no known history of felony charges.

Reed married in Jackson County, which includes some of Kansas City, Missouri, in June of 2019.

His wife filed for divorce in July and a hearing in the divorce case is scheduled for December 2.

The Wyandotte County district attorney’s office was awaiting a police report before it would consider charges against Reed, a spokesman said Tuesday.

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A car that has been parked in the same spot for almost 50 years has become a tourist attraction in an Italian town.

A grey Lancia Fulvia has become a mainstay out the front of a newsstand in Conegliano, in the country's Veneto region.

The owner of the classic car, 94-year-old Angelo Fregolent, parked the vehicle outside the business which he ran with his wife in 1974.

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When the couple retired, they left the vehicle on the street.

The car has since become a local landmark, as tourists snap a photo with the car to upload to social media.

However, those hoping to get a selfie with the local landmark may have to visit sooner rather than later.

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There is a plan to remove the four parking spaces on the busy street where the car is located.

Locals have been discussing moving the vehicle to a place where it can continue to be admired.

As for the original owner, he is pleased with the attention his car is getting and wants to see that admiration continue.

"Of course I would be happy to see it valued as it deserves," Mr Fregolent told local newspaper Il Gazzettino.

The ripples created by massive cosmic collisions have reached Earth after travelling across the universe for billions of years.

Scientists have detected the largest number of these gravitational waves since the cosmic events were first discovered in 2015, according to new research.

Astronomers made 35 new detections of gravitational waves, or ripples in space-time, between November 2019 and March 2020.

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The cosmic waves were largely created by pairs of merging black holes, but several were born of rare collisions between dense neutron stars and black holes.

It's a giant leap from when just three gravitational waves were detected between 2015 and 2016.

This brings the known number of detected gravitational waves to 90 from 2015 to 2020.

They were detected by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, in the US, and the Virgo gravitational-wave observatory in Italy.

The results of the latest observation campaign were published on Monday.

Star life and death

Gravitational waves can help scientists better understand the violent life cycle of stars and why they turn into black holes or neutron stars when they die.

These ripples in space-time were first predicted by Albert Einstein in 1916 as part of his theory of general relativity.

This latest discovery is "a tsunami" and a "major leap forward in our quest to unlock the secrets of the Universe's evolution," study co-author Susan Scott, a professor at the Australian National University Centre for Gravitational Astrophysics, said in a statement.

"This really is a new era for gravitational wave detections, and the growing population of discoveries is revealing so much information about the life and death of stars throughout the Universe," she said.

"Looking at the masses and spins of the black holes in these binary systems indicates how these systems got together in the first place."

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Improving the sensitivity of the detectors to gravitational waves is helping scientists track more of them than before, Professor Scott said.

"The other really exciting thing about the constant improvement of the sensitivity of the gravitational wave detectors is that this will then bring into play a whole new range of sources of gravitational waves, some of which will be unexpected," she said.

Diverse black holes and neutron stars

This new catalogue of gravitational waves includes black holes of all shapes and sizes, in addition to the rare mergers of neutron stars and black holes.

Black holes and neutron stars are both the result of star death.

When stars die, they can collapse into ravenous black holes that consume all of the matter around them.

Or they can form a neutron star, an incredibly dense remnant that remains after a star explodes.

Currently, the heaviest known neutron star is 2.5 times the mass of our sun and the lightest black hole is five times the mass of our sun. In between is the "mass gap."

Improving and refining the detectors is also helping scientists tackle the mass gap, or identifying what exists within this range.

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One of the collisions in this latest observation campaign brought a massive black hole about 33 times the mass of the sun with one of the lowest-mass neutron stars ever found, which is about 1.17 times the mass of our sun.

"Only now are we starting to appreciate the wonderful diversity of black holes and neutron stars," study co-author Christopher Berry, a member of the LIGO Scientific Collaboration, said in a statement.

"Our latest results prove that they come in many sizes and combinations.

"We have solved some long-standing mysteries but uncovered some new puzzles too.

"Using these observations, we are closer to unlocking the mysteries of how stars — the building blocks of our universe — evolve."

Dr Berry is also a lecturer at the University of Glasgow and a visiting scholar at Northwestern University's Center for Interdisciplinary and Exploratory Research in Astrophysics, or CIERA.

The LIGO and Virgo detectors will be joined by the Kamioka Gravitational Wave Detector project in Japan for the next observing run scheduled to begin in late 2022.

Until then, scientists around the world will study the latest observations to look for intriguing signals that may be hiding in the data.

"It turns out that the gravitational-wave universe is incredibly exciting," Maya Fishbach, a NASA Einstein Postdoctoral Fellow at CIERA and member of the LIGO Scientific Collaboration, said in a statement.

"Our upgraded detectors will be able to catch quieter signals, including black holes and neutron stars that merged even farther away, with signals from billions of years ago.

"I can't wait to discover what else is out there."