The New Castle County Courthouse in Wilmington has reopened for business, 3 days after that deadly shooting in the courthouse lobby. Now, word is coming out the investigation of the shooting is widening.

An affidavit to search the home of a Texas man who killed his former daughter-in-law at a Delaware courthouse says the man's son and wife are also suspects in her death.

Thomas Matusiewicz shot Christine Belford and her friend Monday at the New Castle County Courthouse after Belford arrived for a hearing in her lawsuit against the family. He then killed himself.

According to the affidavit, Matusiewicz, his wife and his son are "suspected of intentionally and knowingly participating in a murder." It describes video that shows Matusiewicz and his son hugging in the courthouse lobby.

After the son left, Matusiewicz waited for his victims, killed them and wounded two officers before shooting himself. Two handwritten death certificates for Belford and her lawyer were found on his body.

The Associated Press and the News Journal also report authorities were working Tuesday to understand how the killings were planned, questioning former optometrist and convicted kidnapper David Matusiewicz about his father and searching the older man's home in Edcouch, Texas. The yard of the small single-story home was filled with a crime scene investigation truck and unmarked grey pickup trucks commonly driven by federal agents.

Texas Sheriff Lupe Trevino said they were searching the premises on a request from Delaware authorities.

Strife over the divorce, custody battle and kidnapping stretched back years. In a bankruptcy filing in Texas last year, Thomas Matusiewicz noted that he and his wife, Lenore, along with his son and daughter, Amy Gonzalez, were defendants in a Delaware Superior Court lawsuit filed by Belford.

Amy's husband, Juan Gonzalez, said the acrimony had stressed out the entire close-knit family, but that they were shocked by Monday's shooting. Gonzalez said Lenore Matusiewicz told his wife she saw no signs that her husband was planning violence.

Gonzalez said he last saw Thomas Matusiewicz about a week ago as the family was preparing to drive east for Monday's court hearing and to visit a family member in New Jersey.

"I guess Tom had other plans," Gonzalez said. "We're still trying to figure out why he did that."

Gonzalez said his wife told FBI officials that her father had a brain tumor that went untreated for years and she wondered if it could have played a role in the shooting.

"He was changing, forgetting things," Gonzalez said.

WPVI/6 ABC talked exclusively to Lenore Matusiewicz Wednesday night. She confirmed her husband was in possession of the anti-lawyer book, Kill All Lawyers. "A man I know from Florida had sent us that book; he had a lot of legal problems," Lenore said.  

Court documents also say two death certificates were found on Thomas Matusiewicz's body after he took his own life, one with Belford's name on it and the other with her lawyer.

But Lenore says on Monday, there wasn't a hint of evidence Thomas was going to commit murder.  

"I would have stepped in front of the gun; I didn't want anybody dead," Lenore said.

She said she wished she could have done something to stop it.

The Associated Press contributed to this report.