La. officers who killed boy accused of excessive force before

New details reveal past legal troubles of the two Louisiana police officers charged with killing a six-year-old boy, including a pending civil lawsuit for excessive force.

But more than six days after the deadly incident, investigators are still trying to figure out what sparked it, reports CBS News correspondent David Begnaud.

An Avoyelles Parish Judge charged Derrick Stafford and Norris Greenhouse Jr. with second degree murder Monday. They are now in isolation in jail and being held at $1 million bond.

The arraignment comes nearly a week after six-year-old Jeremy Mardis was gunned down in his father's SUV following a police chase.

Video from an officer's body camera appears to show Christopher Few with his hands in the air. Both officers opened fire, killing Mardis who was buckled into the passenger seat next to his father.

State investigators are still trying to determine why city marshals opened fire on Few, who appeared to be unarmed.

Last week, Megan Dixon, who claims to be Few's fiancée, told CBS News that she argued with Few the night of the shooting. She also said Few knew at least one of the deputies.

"It was Norris Greenhouse in the US Marshal car. He knows Chris. He don't like Chris," Dixon said.

Stafford and Greenhouse were named in a civil lawsuit, claiming they used excessive force in a 2013 arrest, along with four other Marksville police officers. The case is still pending.

Thirty-two-year-old Stafford was also allegedly indicted on two separate rape charges in 2011, but both cases were dismissed.

Latasha Murray knows the family and says the incident is troubling.

"It's just a lot of stuff's been swept up under the table and it's sad that an innocent six-year-old life had to be taken for... for something to be done about it," Murray said.

Avoyelles Parish Sheriff Doug Anderson disagrees.

"There's no dirty business that happens around here," he said.

On Monday, Mardis was buried in Hattiesburg, Mississippi, the town where he spent most of his short life.

"You don't want to believe it's real," said Miranda Sigler, who became his babysitter when he was 10 months old. "I'll always miss him. I don't want to fathom going on without seeing him again."

Investigators issued a gag order on Monday, asking witnesses and victims not to speak to the media.