• With the major prosecution witnesses now finished testifying at Bill Cosby’s trial on sexual assault charges, who will the defense introduce soon as part of its rebuttal? Mr. Cosby has said he will not testify. Might he change his mind?

• The prosecution plans to call a forensic toxicologist to testify about the effects of quaaludes and other drugs, which prosecutors say Mr. Cosby used to incapacitate women.

• On Thursday morning, the prosecution introduced two supporting witnesses, a police officer who interviewed Mr. Cosby in 2005 and a neighbor of Andrea Constand, the former Temple University staff member who says Mr. Cosby drugged and sexually assaulted her in early 2004. He said Ms. Constand became more distant in the early months of that year, before she left Temple.

• Mr. Cosby was accompanied to court by show-business friends, but for the fourth straight day there was no sign of his wife, Camille Cosby.

The police officer who interviewed Mr. Cosby in 2005 said the entertainer described the sex as consensual.

Sgt. Richard Schaffer of the Cheltenham Township Police Department, had interviewed Mr. Cosby at a New York law office. He read from Mr. Cosby’s police interview at the time and said the entertainer had described the sexual encounter as just “petting and talking.”

During cross-examination, Brian J. McMonagle, Mr. Cosby’s lawyer, led Sergeant Schaffer through Ms. Constand’s statements to the Canadian and Pennsylvania police, emphasizing the different dates, details and omissions in her accounts about the night of the alleged assault and other meetings.

Mr. McMonagle pointed out in court that Ms. Constand had reviewed and crossed out parts of her statement after one Pennsylvania police interview, removing things that she did not want to be part of it. As an example of one thing she crossed out, he cited a remark in the police notes that recorded her saying to Mr. Cosby, “I told him that the cognac was fantastic.”

Sergeant Schaffer said complainants have a right to amend a statement before finalizing it, though he said his notes of the interview — even those crossed out — had been accurate.

The questioning of Sergeant Schaffer was tense at times.

Mr. McMonagle sought to use Mr. Cosby’s police interview to suggest that the entertainer had described a romantic, consensual relationship, one in which Mr. Cosby acknowledging backing off at one point when, the entertainer said, Ms. Constand balked at his sexual advance.

Sergeant Schaffer bridled somewhat.

“He was a real gentleman there,” he replied.

Mr. McMonagle then noted for the jury that the district attorney in 2005, Bruce L. Castor, had investigated Ms. Constand’s complaint and subsequently decided against bringing charges, citing insufficient evidence. Ten years later, though, the Montgomery County district attorney’s office revisited that decision, in part, it has said, because in 2015 it saw the Cosby deposition in which he admitted obtaining quaaludes to seduce women.

During his cross-examination, Mr. McMonagle returned to a topic the defense has used to suggest Ms. Constand acted in ways inconsistent with that of a person who has been sexually assault. He mentioned again her 53 calls to Mr. Cosby in early 2004, around the time when she says she had been sexually assaulted. He said Ms. Constand placed at least two calls to Mr. Cosby on Valentine’s Day that year.

Ms. Constand had said that the number of calls is inflated by the difficulty she sometimes had getting a hold of Mr. Cosby, and that returning his calls was part of her job because he was a Temple trustee.

But M. Stewart Ryan, an assistant district attorney, said these calls were sandwiched between calls to the Temple women’s basketball coach, suggesting Ms. Constand was discussing university business with Mr. Cosby. And he asked Sergeant Schaffer what they might have talked about.

Sergeant Schaffer said he would guess, “Basketball.”

A drug expert is expected to be a major witness for the prosecution.

Mr. Cosby’s lawyers tried to stop his appearance, but Judge Steven T. O’Neill has ruled that his testimony can go forward. The expert, Dr. Timothy Rohrig, an adjunct professor at Wichita State University, is likely to tell the court that the effects reported by Ms. Constand regarding the three pills Mr. Cosby gave her on the evening of the alleged assault are consistent with the effects of Benadryl or quaaludes.

Ms. Constand says she was drugged and assaulted at Mr. Cosby’s home near Philadelphia in 2004.

We still haven’t heard the deposition testimony Mr. Cosby gave in 2005, where he admitted to obtaining quaaludes to have sex with women. Prosecutors have to decide when to introduce that.

Do marital optics matter to sex assault trial juries?

Some criminal-trial experts think they do and say that Mrs. Cosby’s absence from the courtroom for the last four days may have hurt him.

“Her absence could be interpreted by them as an unwillingness to sit and listen to very unpleasant truths,” Joseph McGettigan, a former federal prosecutor who attended the trial, said Wednesday.

He said it was unlikely that the whole jury would focus on her absence, but that it was “entirely possible” that one or two jurors would do so.

In 2014, when the accusations of sexual assault against Mr. Cosby began multiplying, Mrs. Cosby defended him as a “wonderful husband, father and friend” and chastised the media for failing, she said, to subject the accounts to proper scrutiny. More recently, Mrs. Cosby, 73, has not spoken out publicly about Mr. Cosby, though sources close to the family have cited her continuing support in some recent news accounts, and suggested she may appear later in the trial. The two have been married since 1964.

A spokesman for Mr. Cosby, Andrew Wyatt, declined to comment on whether that was the plan. “Not at liberty to discuss our strategies,” he said.

Mr. Cosby has been accompanied to court each day by various friends, including Keshia Knight Pulliam, who played a daughter of his on “The Cosby Show.”

Alan Tauber, a Philadelphia defense attorney, said he thinks the jurors will look past the issue of Mrs. Cosby’s absence.

“While it is always preferable to have family members sitting behind the defendant in support,” he wrote in an email, “I think the gravity of this case and the sense of public importance the jurors no doubt feel with respect to their job wholly marginalizes those factors.”

Also expected to testify for the prosecution, an expert on sexual assault victims.

In particular, the expert would be asked by prosecutors to talk about the sort of behavior, like memory loss, that sexual assault victims sometimes display after they have been attacked. This testimony could be used by the prosecution to counter defense questions about why, for example, Ms. Constand gave some inconsistent statements to police and why she took nearly a year to come forward.

The jury could be asked to begin deciding the case early next week.

On Wednesday, just three days into the trial, Judge O’Neill gave an upbeat assessment of how quickly the court was hearing from witnesses and going through other evidence. “We think we are moving a lot faster than two weeks,” he said.