An elderly Ottawa priest in failing health is charged with three counts of indecent assault related to sexual offences alleged to have taken place between 1970 and 1976.

Father William Joseph Allen, who is also known as Father Bill, was arrested on Monday and released on conditions.

Allen was ordained to the priesthood in 1955. Over the years, he served at several Ottawa churches and taught at St. Pius X High School where a yearbook from the 1970s regards him as the "friendly friar." While at St. Pius, Allen taught both history and French.

Ottawa police started their investigation in March 2010 after a victim came forward with allegations of a series of inappropriate incidents between a Catholic priest and two teenage boys in Ottawa. The second victim was identified during the course of the investigation, police said.

Although Allen is charged with indecent assault, police say it is equivalent to the modern-day sex assault charge.

Police say even though two victims have been identified, there is always the possibility that more victims will come forward.

Allen withdrew from active ministry several years ago. He is now suspended and prohibited from presenting himself as a Catholic priest.

In a statement Monday, Ottawa Archbishop Terrence Prendergast acknowledged the charges.

"I am deeply saddened to hear that criminal charges, on the basis of sexual assault, have been laid against Fr. William Allen, one of our priests," Prendergast stated.

"I invite Catholics, and other people of goodwill, to pray with me for a process of justice, as well as one that will bring healing and reconciliation to victims."

Prendergast says he's confident the judicial process will shed light on the circumstances that led to the charges: "Justice must be done, and must be seen to be done," he stated.

In early June, Prendergast told CTV Ottawa the Church is trying to be transparent when it comes to dealing with sex abuse.

He said he wants church-goers to feel free to speak up about any problems they may have with church officials.

Investigators urge anyone with information about the case to come forward by contacting Ottawa police at 613-236-1222, ext. 5944 or Crime Stoppers at 613-233-8477 (TIPS).

With files from CTV Ottawa's Kate Eggins