Was there some flaw in the way the police stopped him and administered the breath-analysis test? Was it the way he was arrested and searched?

There was an outcry after prosecutors withdrew criminal charges against Rahim Jaffer yesterday, leaving legal observers wondering what went wrong for the authorities after police intercepted the former Tory MP on an Ontario rural road last fall.

Mr. Jaffer pleaded guilty in Ontario Court of Justice to careless driving, a Highway Traffic Act offence. The Crown dropped criminal charges of cocaine possession and having a blood-alcohol level above the legal limit. A speeding charge was also withdrawn.

“Any one of 50 things could have gone wrong here,” said Mark Ertel, former president of the Defence Counsel Association of Ottawa. “It's pretty rare that these things do go wrong, but there are mistakes that could be made.”

The case was sealed three weeks ago at a pretrial conference. At the off-the-record meeting, attended by a different judge from the one who would hear the case, defence lawyer Howard Rubel made arguments that led the Crown to decide it couldn't pursue criminal charges against his client.

“There was no reasonable prospect of conviction,” Crown attorney Marie Balogh said in court yesterday.

Saying he was “reading between the lines” of the Crown's remarks, Mr. Justice Douglas Maund told Mr. Jaffer: “I'm sure you can recognize a break when you see one.”

The former MP was sentenced to a $500 fine. He also agreed to make a $500 charitable donation.

Ms. Balogh wouldn't comment further. “There were issues related to the evidence,” Brendan Crawley, a spokesman for the Ontario Ministry of the Attorney-General, said in an e-mail.

The cocaine charge was embarrassing for Mr. Jaffer, 38, who campaigned in the last election for drug-free schools.

But Mr. Ertel said it is the blood-alcohol charge that the Crown would have prosecuted more vigorously, because it is considered more dangerous to the public. This, he said, suggested there was a problem with the way Mr. Jaffer's breath sample was collected.

Alan Young, a professor at York University's Osgoode Hall Law School, said some prosecutors have been plea-bargaining drunk-driving cases to careless-driving charges because of uncertainty with the law.

In 2008, Ottawa eliminated the “two-beer defence,” where drivers argued their alcohol tests were wrong. Now, drivers have to prove the machine malfunctioned. Prof. Young said defence lawyers are expected to challenge the new rule in the Supreme Court.

Mr. Jaffer was arrested in September after a 10-year Ontario Provincial Police veteran, Constable Kim Stapleton, clocked him going at 43 kilometres an hour over the speed limit in Palgrave, north of Toronto. She stopped him, smelled alcohol and took a breath-analysis sample at the roadside. The court heard that Mr. Jaffer told the officer he had had two beers.

He was arrested and searched.

However, the court yesterday heard no mention of the cocaine charge.

“I'm sorry. I know this was a serious matter,” Mr. Jaffer said outside court yesterday. “I know I should have been more careful and I took full responsibility for my careless driving.”

With a report from Bill Curry in Ottawa