Sanchez is being questioned by Internal Affairs, which in a rare move is handling both probes - into Vera's slaying and Dove's alleged role.
Sanchez's lawyer did not return phone calls.
Dove, a 16-year veteran who has been in homicide since 2005, has been removed from street work.
After examining Dove's phone records and other evidence, investigators believe the detective drove Sanchez to a hotel in Rochester the day after Vera's death, sources told The Inquirer last week. The records showed Dove purchased a room for her with his credit card.
Investigators believe Dove visited Sanchez at the hotel two weeks later, though he told investigators he did not know Sanchez's whereabouts.
Dove left work early on the night of Vera's killing. He went to the scene before Vera's body was found and moved Sanchez's car, the sources said.
In a statement to Internal Affairs this month, Dove volunteered that he had moved Sanchez's car, but said he was unaware of Vera's death, the sources said.
He only moved it, he told investigators, because Vera had a history of stealing it. Dove said he could not remember where he had moved the car to, and police have not recovered the vehicle.
Police first became aware of Dove's connection to Sanchez days after Vera's death, when he told the detective assigned to the case that he knew Sanchez and could help bring her in for an interview.
He also asked the detective to "go easy on her," the sources said.
In the initial interview with investigators, Dove said that he gave Sanchez money for a lawyer, but that he did not know where she was. He lost contact with her after she stopped answering her phone, he said. He also said he was in love with her.
Days after Dove's statement, his phone and credit card revealed details about the trip to New York, the sources said.
Dove has told colleagues that he helped Sanchez flee because friends of Vera wanted revenge.
As part of their investigation, Internal Affairs interviewed police and prosecutors. The department's findings will be presented to the District Attorney's Office, which will decide whether Dove committed any crime.
Vera and Sanchez had a violent relationship.
In April, Vera, a construction worker, was arrested after Sanchez said he stole $70 from her, slammed her head against the dashboard of a car, and punched her numerous times in the face.
Vera was arrested again in July, for allegedly trying to burn Sanchez's hair on a kitchen stove, telling her, "You are going to regret this one."
Both cases fell apart after Sanchez failed to testify.
Witnesses have told police that on the night of the stabbing, Vera and Sanchez had been at a block party at Fifth and Westmoreland Streets and had been fighting throughout the evening. At one point, they said, Vera pulled Sanchez from a car, where she had been sitting with another man, and punched her.
They were still arguing hours later, police believe, when she stabbed him in the chest. Vera made his way into an empty speakeasy, where he died. His body was found hours later.
Phone records show Sanchez called Dove around the time of the slaying.