UPDATE: This story was updated April 3, 2013, to add the news of a charge laid against former Guelph Conservative campaign worker Michael Sona and to update some information below.

In 2011, Elections Canada investigators began probing calls placed to voters in Guelph, Ont. in the final days of the 2011 federal election that wrongly claimed to be from Elections Canada. The calls redirected voters to a polling station they couldn't use.

It's illegal both to interfere with a person's right to vote and to impersonate Elections Canada.

Now, with word that former Guelph campaign worker Michael Sona faces a single charge in the affair that has come to be know as the robocalls scandal, here's a look at what we know about the case, according to court documents and information provided in interviews:

1. Elections Canada investigator Al Mathews started looking into complaints in Guelph on May 5, 2011, three days after the election that saw reports of illicit phone calls. The winning candidate in the riding, Liberal Frank Valeriote, compiled a list of almost 80 names of people complaining about the calls. News of the investigation didn't break until Feb. 22, 2012.

2. All political parties use automated robocalls and live calls to identify voter support and contact people during a campaign. The campaign of Guelph Conservative candidate Marty Burke used RackNine, a company that offers voice broadcasting services, to make legitimate robocalls to campaign supporters. The person who made the fraudulent robocalls also used RackNine.

A demonstrator protests in Montreal against fraudulent election calls. (Graham Hughes/Canadian Press)

3. The person who made the calls used a disposable, or burner, cellphone, registered to a "Pierre Poutine." The RackNine charges were paid via PayPal using prepaid credit cards, purchased at two Shoppers Drug Mart stores in Guelph. Shoppers Drug Mart doesn't keep its security camera videos long enough to see who bought the cards more than a year ago.

4. Elections Canada traced the IP address used to access RackNine on election day and send the fraudulent message. Mathews got a court order for Rogers, the company that provided the internet service to that IP address, to provide the customer information that matches that address, on March 20, 2012.

5. Pierre Poutine and Burke campaign worker Andrew Prescott accessed their RackNine accounts using the same IP address. On election day, they accessed their RackNine accounts from the same IP address within four minutes of each other, Mathews says in documents filed in court.

6. A court document lists the billing account numbers for the customer information provided by Rogers to Mathews. Those accounts don't match the number found on the Burke campaign's Rogers invoices submitted to Elections Canada, suggesting RackNine wasn't accessed through a computer in the Burke campaign office.

7. Two Conservative staffers, accompanied by the party's lawyer, told Mathews they overheard Michael Sona, another Burke campaign worker, talking about "making a misleading poll moving call." Sona, who stepped down from a job in the office of Conservative MP Eve Adams when the story broke, has previously said he had nothing to do with the misleading calls. Mathews later corrected the record, adding a footnote to a subsequent court document that said campaign worker Matthew McBain actually described Sona suggesting an autodial call "that would not track back to the Burke campaign," not a misleading poll moving call.

8. Arthur Hamilton, the Conservative Party's lawyer, told Mathews the list of phone numbers uploaded to RackNine by Pierre Poutine appeared to be a list of identified non-Conservative supporters, with data on it that was updated in CIMS, the party's database, days before the election. The CBC's Terry Milewski had reported a similar pattern after sifting through complaints in 31 ridings.

9. News coverage led to 40,000 people contacting Elections Canada one way or another — whether to report a misdirecting call or by signing an online petition to express concern that it had happened — chief electoral officer Marc Mayrand told a parliamentary committee in April. There are now specific allegations in almost 200 ridings by 800 people. As of April 3, 2013, Elections Canada is investigating 1,399 complaints in 247 ridings.