DETROIT -

Just days after the 9/11 terrorist attack, with the entire world on edge, a man showed up at Detroit's federal building with a loaded gun.

That man's parents now want answers after their son's prison death was ruled a suicide.

There were thousands of federal workers inside the 27-floor building, dozens of their children in a day care center, when David Sera walked into the building and shot lobby Officer Ronald Sheffield, who returned fire. Sheffield did not survive.

"He (David) got shot five times," said Samuel Serra, David's father. "I didn't think he was going to live, but he did."

David's mother and father said before their son was a cop killer he was a normal, lovable, little boy, growing up in Chesterfield Township.

"A real joy, very good, happy, smiling all the time," said Loretta Sera, David's mother. "He loved the sports. He played football and basketball and soccer, he had friends, was happy. After high school he joined the the Navy. That's when he began having manic mental health issues, extreme paranoia."

"He had a fear of the government," said Samuel. "He thought the government was after everybody."

David came home after being in the Navy and lived with his parents. His parents said when he was on his meds, things were fine, but not when he was off his meds.

"His mannerisms changed, he made excuses why he didn't want to go to work and, you know, just everything started changing," said Samuel.

On Sept. 11, 2001, terrorists attacked America. Thousands of innocent people died. America was deeply impacted. According to David's parents, he the worse.

"He just had this fear of the government," said Samuel. "And when he saw that 9/11 attack he just, I know that kind of set him off, but I didn't know how bad."

Ten days later David walked into the federal building in Detroit with a gun in his bag and killed Sheffield..

"I had the radio on, and I heard all what was going on downtown, and something in my mind just told me, 'gosh, I think that was my son,'" said Samuel.

Officer Sheffield was working the metal detector at the building that day. The father of two girls took the security job after protecting Americans as a Marine during the Persian Gulf War. David shot Sheffield for no apparent reason.

"That devastated us," said Samuel. "To think that my son cost a man his life, that hurt, hurt bad."

The Sera family said the reason the shooting happened is because David was mentally ill and off his meds.

David was found guilty and sent to prison, but there was one up side -- he was back on medication.

"His mind was good," said Samuel. "I mean, he got back into playing sports, he was taking a machinist apprenticeship, but in the prison systems, if you're not a threat to yourself or others, they don't force you to take medication."

David was transferred to a new prison in California and put into general population. There he could choose whether to take his meds or not -- he chose against it.

"I just got a phone call Nov. 14 that they found David unresponsive in his cell. That's all they told me," said Samuel. "The next day I got a call from the coroner telling me he had taken his own life. "

David's cellmate said he doesn't know what happened.

"I knew my son and he told me he would never take his own life," said Samuel.

The prison will not give the family any reports, photographs or findings of their investigation, and the family is now wondering why.

"Most of the inmates he was with were all drug offenders, bank robbers, very few murderers, especially someone who murdered a police officer or federal agent," said Samuel. "The guards don't take kindly to those kind of people.

While the Seras grieve for their son David, they grieve for Sheffield, and think both lives could have been saved if mental illness were taken seriously.

"There has to be a lot more help for our mentally ill people," Loretta said. "A lot more. And I'm hoping somehow we can find some more help in this tragic."

"Just because financially they can't afford to take care of themselves or get the medication they need, there should be places there they can go for this help," said Samuel.

Before 1990, mentally ill people went to state hospitals. When they shut down, many patients went home to their families, some to the streets. Thousands committed serious crimes. David's is just one story.

Today there are more than 700,000 thousand mentally ill people locked up behind prison walls.

Click here to donate to the National Law Enforcement Memorial Fund in the name of Officer Sheffield.

Donations in the name of Dave Serra:

National Alliance on Mental Illness

28304 Aline Drive

Warren, MI 48093

Mental health resources:

http://www.michigan.gov/documents/MDCH-MentalIllness-10AUG04_102671_7.pdf

http://www.michigan.gov/mdch/0,4612,7-132-2941_4868_4899---,00.html

http://namimi.org/

http://www.amioakland.org/

Contact Michigan lawmakers:

http://michigan.sierraclub.org/semg/SEMG-Contact_Gov.htm