JOLIET, Ill. (CBS) — In a major development in the murder trial of Drew Peterson, the judge has reversed himself and barred the testimony of a key prosecution witness.

Earlier, Judge Edward Burmila said Army Capt. Scott Rossetto could testify about a conversation he had with Stacy Peterson, just before she disappeared.

But confusion over the date of the conversation and a mistake in an email prosecutors sent to the defense lawyers prompted the judge to bar the testimony.

Rosetto was a friend of Peterson’s missing fourth wife, Stacy. He briefly took the stand, but the defense objected when it was learned that there was confusion about when and where the conversation between the two took place.

That discrepancy led the judge to bar him from testifying further.  Rosetto, who was flown from Germany to take the stand, told CBS 2′s Mike Puccinelli he was disappointed he was barred from testifying.

“If I’m not allowed to testify, then Stacy’s secret dies with her,” Rosetto told Puccinelli.

Peterson, a former Bolingbrook police sergeant, is charged with the murder of his third wife, Kathleen Savio, whose body was found in a dry bathtub on March 1, 2004. Her death was initially ruled an accidental drowning, but was reclassified as a homicide following an exhumation and new autopsy after Stacy Peterson disappeared in 2007.

Rosetto said Stacy Peterson called him out of the blue weeks before her disappearance, and they exchanged text messages. Drew Peterson caught them at a Denny’s and sat down in his police uniform.

Rosetto, who traded raunchy text messages with Stacy shortly before she disappeared in 2007, testified at a pre-trial hearing that he had a conversation with Stacy in which she said Drew Peterson coaxed her into providing a false alibi for Drew on the weekend of Savio’s death.

On Thursday, Dr. Larry Blum, the pathologist who conducted the second autopsy on Savio, testified that based on his analysis, her death was a homicide. He said a gash on the back of her head and several bruises on the front of her body could not have been the result of a fall in the tub. He explained someone falling accidentally wouldn’t have suffered injuries on both the front and back of their body.

Blum also noted Savio had no bruises or injuries to her arms that would indicate she tried to stop herself from falling.

He also pointed to the lack of drugs or alcohol in her system, saying adults don’t drown in bathtubs unless they are intoxicated, or have physical maladies that would incapacitate them.

But defense attorneys have said three pathologists they hired all said the injuries could have resulted from a fatal slip and fall in the tub.

Blum acknowledged the first pathologist who performed an autopsy – and ruled her death an accident – was well-regarded professionally. Blum also acknowledged he relied a great deal on Dr. Bryan Mitchell’s autopsy report in performing a second autopsy in 2007, although he reached a different conclusion. Mitchell has since passed away.