Eight people charged in Ontario's worst mass slaying will stand trial on all charges, a judge has ruled.

Six men each face eight counts of first-degree murder, and a man and a woman are charged with being accessories after the fact following the discovery of the bodies of eight Bandidos gang members last April in a farmer's field near the small town of Shedden.

Justice Ross Webster's decision on Thursday marks the official end of a long, secretive preliminary hearing for the accused that began in January to determine whether there was enough evidence to send the eight to trial.

At least two defence lawyers say the evidence warranted reduced charges for their clients, and are considering asking for another court to review the judge's decision.

"I suspect that just about every person will be seeking authorization to proceed with a review of this decision to see if it is, in fact, legally on solid ground," said Tony Bryant, who is representing Marcelo Aravena, charged with first-degree murder.

A review would delay a trial by several months.

"On a review, if there's a different result then the Crown can go to the Court of Appeal, or the accused can go to the Court of Appeal. Depending on what happens there, there's a possibility to get permission and go all the way to the Supreme Court of Canada," said Don Crawford, who is representing Michael Sandham, also charged with first-degree murder.

A long delay could change the location of the trial, Crawford said.

"This case supposedly is in St. Thomas [Ont.].  Courtroom facilities aren't available there, but there's talk of a new courthouse in St. Thomas and then by the time this thing comes to trial, there'll be a new courthouse in St. Thomas."

All eight accused are scheduled to appear in court July 11, though if reviews of the decision are launched, the appearances could be postponed until fall or later.

Those charged with first-degree murder include:

• Wayne Kellestine, 57, Dutton-Dunwich Township.
• Frank Mather, 33, of Dutton-Dunwich Township.
• Brett Gardiner, 22, of no fixed address.
• Michael Sandham, 38, of Winnipeg.
• Marcelo Aravena 30, of Winnipeg.
• Dwight Mushey, 39, of Winnipeg.

A common-law couple — Eric Niessen, 45, and Kerry Morris, 47, of Monkton, Ont. —face charges of being an accessory after the fact. First-degree murder charges against the two were dropped last May.