Devan Hawkes, an employee of the state Corrections Department who investigates gangs, cited letters found at the couple's home and in the cells of two inmates belonging to the Aryan Brotherhood prison gang.
Letters from Robert Noel showed active involvement in a "Dog O' War" business, Hawkes said.
Noel and his wife, Marjorie Knoller, both lawyers, are charged in the Jan. 26, 2001, mauling of their neighbor Diane Whipple by two big Presa Canario dogs they kept in their San Francisco apartment. The trial was moved to Los Angeles due to extensive publicity in San Francisco.
Knoller, 46, who was walking one of the dogs at the time of the attack, is charged with second-degree murder, involuntary manslaughter and having a mischievous animal that killed a human being. She faces up to 15 years in prison if convicted.
Noel, 60, faces the latter two charges and up to four years in prison if convicted.
On Thursday, jurors saw on a screen enlarged portions of letters in which Noel appeared to encourage Pelican Bay State Prison inmate Paul "Cornfed" Schneider to try to escape and said that if he and Knoller were present they would help.
"I would want to make it clear," Noel wrote, "... If you went for the door, all she and I would do is wave you goodbye and wish you godspeed."
Hawkes also identified a letter from Noel that named and pinpointed the location of an inmate who had dropped out of the Aryan Brotherhood.
"There is a potential danger," Hawkes said. Noel "is identifying the location of a potential witness, and the potential is that bodily harm could come to this witness."
Hawkes said Schneider and another inmate worked with Noel and Knoller on a business to raise fighting Presa Canarios.
Prosecutor Jim Hammer showed jurors invoices for books ordered by the prisoners — among them "Gladiator Dogs," "Fighting Dog Breeds," and "Manstopper: Training a Canine Guardian."