The sexual assault trial of Halifax lawyer Lyle Howe continued into its third week Tuesday as the jury heard more toxicology evidence.

Howe has pleaded not guilty to sexual assault and administering a stupefying drug. The charges were laid after an alleged incident on March 20, 2011, involving a 19-year-old woman.

Toxicologist Christopher Keddy continued his testimony Tuesday.

Last week Keddy told the court traces of codeine and morphine were found in the woman's urine when samples were taken about 24 hours after the alleged assault in March 2011.

On Tuesday he was questioned by both Crown and defence about those levels. He said taking one or two tablets of codeine, which breaks down into morphine, could account for the levels found in the complainant's urine.

The codeine could have been taken up to a day before the incident. Keddy said he ultimately didn't think codeine caused the effect the complainant described: blackouts, memory loss and the feeling of being deeply drunk.

He said a much more likely cause was alcohol. Keddy also said there are a few drugs that would not have shown up in blood or urine tests 24 hours later.

He said one of those is the date rape drug GHB. No test was done for that drug as the window for finding it had already passed.

The last of the Crown's witnesses, the principal police investigator in the case, took the stand Tuesday afternoon.