HOUSTON -- The parents of a murdered doctor filed a wrongful death lawsuit Wednesday afternoon against their former daughter-in-law and a pharmaceutical company, Local 2 reported.

Police said Rick Lohstroh's 10-year-old son fatally shot him outside his ex-wife's Katy home on Aug. 27 as he picked him and his 8-year-old brother up as part of a joint custody agreement.

Lohstroh's parents -- Richard and Joanne Greene -- filed a lawsuit against Deborah Geisler, the boy's mother, and the maker of Prozac, Ely Lilly and Co.

"Today we are filing suit on behalf of Dick and Joanne Greene for the tragic death of their son, Rick," said David Matthews, an attorney.

Lohstroh's parents and friends said Rick Lohstroh was upset with Geisler for putting their son on Prozac, which happened one month before his death.

"In the week prior to the shooting, the boy's doctor increased his dosage of Prozac. This is really important for two reasons," Matthews said.

Matthews said studies show a change in dosage can lead to violence and the drug's adverse effects are more severe in children.

The 12-page lawsuit argues that Ely Lilly and Co. is to blame for Lohstroh's murder.

"There's a mountain of literature that shows that this drug can cause mania and ultimately violence, certainly in a child," Matthews said.

One page is devoted to blaming Geisler.

The lawsuit names Geisler for not securing her gun, and, as a registered nurse, it said she should have monitored her child's medication more carefully.

"The fact that she is a nurse -- I think that it probably increases her level of understanding and knowledge concerning the drug," Matthews said.

The lawsuit also named Mathew Swanson, Geisler's husband. He owned the home where the shooting took place and where the gun was kept.

Because of the publicity surrounding the shooting death, a Galveston judge put a gag order in place on Sept. 15.

Lohstroh's 10-year-old son remains in juvenile custody but has not been charged with a crime yet. His 8-year-old son is in the custody of his parents after a Galveston judge granted them custody.

The Harris County Sheriff's Department said the 10-year-old retrieved a gun, climbed in the back seat and began shooting "through the back of the driver's seat, striking his father."

Deputies said the boy got out of the vehicle and continued firing before going inside the home, where his mother took the gun from him.

Investigators said it is still a mystery as to why the boy would kill his father, a 41-year-old physician at the University of Texas Medical Branch in Galveston.

During the couple's divorce trial, Geisler accused Lohstroh of sexually abusing their two sons. Two separate police agencies investigated the claims, but neither filed charges.

People close to Lohstroh and his children say Geisler used a form of brainwashing, known as Parental Alienation Syndrome, during the couple's contentious breakup that they believe possibly led to the father's death.

Previous Stories:

September 14, 2004: Caretaker Asks For Gag Order In Slain Doctor Case
September 13, 2004: Slain Father's Son To Remain In Juvenile Custody
September 10, 2004: Friends Blame Brainwashing For Doctor's Death
September 9, 2004: Grandparents Get Custody Of Boys After Father Shot
September 2, 2004: Mother Disputes Report She Made Death Threat
September 1, 2004: Slain Doctor Told Police Wife Threatened To Kill Him
August 31, 2004: Girlfriend, Colleagues Defend Slain Doctor
August 30, 2004: Boy Suspected Of Fatally Shooting Father To Remain Detained
August 27, 2004: Constables: Boy, 10, Shoots Father To Death