ST. LOUIS • The crowd of Angie Young's mourners quickly outgrew the funeral chapel last summer, leaving some to stand in aisles for two hours remembering the single mother who was devoted to her teenage daughter and career caring for the elderly.

Young, 36, had been shot multiple times late the night of Aug. 23, outside a White Castle restaurant.

"Why would someone take the life of this young lady?" asked an uncle of the woman affectionately called "Bug."

Two St. Louis homicide detectives, sitting quietly in the chapel, already had a guess: Young's ex-boyfriend, Leon T. Moss.

For the next five months, they'd build their case against Moss, who along with two others was indicted Jan. 25 in connection with the murder. Court filings provide an inside look at how they did so, using surveillance videos and DNA evidence to link Moss to the other two men, one an accused heavy hitter in the local drug world.

While it is natural for an investigation to focus on people close to the victim, Moss had a particular motive. He was six days away from trial on assault charges that could have put have him in prison for up to 15 years. Young was to be the complaining witness.

They also discovered one big physical clue: Security cameras showed a white Chevrolet Silverado pickup lurking in the hours before the murder, following several car lengths behind Young as she drove to the restaurant, at 3524 North Kingshighway. It cruised through the lot as she went inside.

Two witnesses heard gunshots around 11:40 p.m. One saw the killer fleeing toward a nearby alley; the other saw a man emerge from the alley and jump into the passenger side of a white Chevrolet truck as it sped off.

Detectives checked Moss' name in databases and came up with an address on Fountain Avenue, in a building owned by his now-wife. A white Chevrolet Silverado was parked outside.

A man who lived at the Fountain address told police he recently bought the vehicle from Moss, his employer. He said nobody else had used the vehicle and that it had been sitting outside his home as late as 9 p.m. the night of the murder.

Detectives seized the vehicle to look for blood, fingerprints, footprints and other forensic evidence.

It's not clear when Donald L. White and Christopher K. Spates came to the attention of police. But by September, detectives sought a court order for the men's DNA, to compare with evidence from the vehicle. Police also seized a computer and two cellphones associated with Spates.

In late January, a grand jury named Moss, White and Spates on charges of first-degree murder and armed criminal action in Young's death.

An affidavit for evidence seizures has been sealed at the request of the prosecutor, who cited "concern that the media may seek out public records for information on the investigation and the case," which could compromise it. Spates was the only defendant named in a press release by police.

The police department and Circuit Attorney Jennifer Joyce's office declined to comment.

All that's publicly known of White and Spates is from their rap sheets.

For Spates, 20, of the 4800 block of Cote Brilliante Avenue in St. Louis, it's not much — less than two weeks in jail on a parole violation after a drug conviction.

But White, 29, of the 10700 block of Spring Garden Drive in St. Louis County, has a string of drug and firearms convictions.

In addition, White and others are accused of moving more than 300 grams of heroin across state lines. Court filings say he and a co-defendant were under federal surveillance at least since 2009. The case includes a firearms charge for being a felon in possession of a semi-automatic pistol, which was loaded with Teflon-coated, armor-piercing ammunition.

Moss, 41, has a history of assault and vehicle tampering charges and ostensibly was the detectives' link to White and Spates.

White's attorney, Kristy Ridings, said prosecutors have not yet shared information on Young's murder. She said her client insists he is innocent.

Spates does not yet have an attorney on record.

David Stokely, Moss' attorney on the assault case, said this week that his client has denied any role in the murder. The lawyer said he knows of no connection between his client and the other two defendants.

"I know he's definitely not the one on the (surveillance) video," the attorney added.

Young's relatives, fearing reprisals, spoke only reluctantly to a reporter.

They said Young, who had sole custody of her daughter after a 13-year failed marriage, didn't talk much about her private life. When she died, she had been working at the Westchester House, a nursing home in Chesterfield.

In court filings, police say Young began dating Moss sometime in 2009 and that she and her daughter lived with him for about a year in the tiny St. Louis County village of Glen Echo Park.

In May 2010, officials charged Moss with assaulting Young three months earlier by repeatedly ramming his car into hers. Moss, then listed at the 2600 block of Minnesota Avenue, had shown violence before, continuing through the early 1990s. One time, he drove a stolen vehicle at officers, officials said, and in another he beat a woman with a broomstick.

In 2008, his girlfriend obtained a court order of protection against Moss on claims he beat her with a belt and broom and stomped on her head. That same woman paid his bail on the assault charge regarding Young and later married him.

Stokely said last week that his client and Young had a volatile relationship, and he claimed she fabricated the assault. He said when Young turned up dead shortly before the trial, it actually hurt Moss' case by making it impossible to reveal her lies in cross-examination.

After she died, Moss pleaded guilty in a deal to serve just three years and has been in custody since his Jan. 13 sentencing.

For Young's family, the recent charges raise more questions but also carry the promise of answers.

Explained one, who said she was afraid to give her name: "I just want to go to court and hear what they have to say. … We are hearing so much, but don't know what is true."