OTTAWA -- With three categories of charges being tried, a diverse array of witnesses and a mountain of documents entered into evidence, it can be hard to follow the thread of Sen. Mike Duffy's trial.

Here are some of the key things learned since his fraud, breach of trust and bribery case opened in February in Ontario Provincial Court. The trial resumes Thursday.

The Herculean efforts to make a scandal go away:

When the media began digging into Mike Duffy's living expenses in late 2012 and early 2013, figures inside then-prime minister Stephen Harper's office and his Senate leadership began looking for ways to put a lid on the controversy. There were drawn-out talks among Duffy and key operatives on how he would make the public believe he was going to repay his expenses, while Harper's chief of staff Nigel Wright would secretly cover the $90,000 bill. The Crown wants to prove that Duffy was either the instigator or an equal partner in the plan, while the defence says he was coerced into going along with the scheme.

The Conservative caucus kept Duffy busy:

Duffy is facing several charges related to travel expenses he claimed while zipping around the country to a variety of events which he said were Senate business. Many of those events were organized by Conservative MPs, some of whom told the court that the former broadcaster was a popular draw for fundraisers. Often the cost of the travel was many times higher than the funds raised. Duffy's lawyer has argued the Senate lists partisan activities as "inherent and essential," while the Crown is trying to prove the senator defrauded the public by dressing up personal or political events as legitimate Senate work.

The strange business of Senate contracts:

Duffy awarded his friend Gerald Donohue $65,000 worth of contracts for research and consulting, which the Crown has framed as a slush fund. Some of that money was later paid out through Donohue's family business to other Duffy service providers, including a personal trainer, an intern and a makeup artist. The defence says the payments might have been unorthodox, but they did not constitute fraud -- no kickbacks or favours were ever requested in return.

Those darned Senate rules:

The dullest part of the trial for observers, but perhaps the most important for Duffy, are the details around the Senate's expense rules. The court has heard that there was no clear definition of what constituted residency when Duffy was appointed to the chamber. Senators had broad discretion to award contracts with little oversight after the fact to determine if the services were delivered. The rules around what constituted Senate business for travel were also vague. Prosecutors have tried to make the case that some of the issues are just matters of common sense, such as where a person actually has their primary residence.