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OK, back to the question.
"There's a mystery in the office, and I just can't seem to make heads or tails of it," Mary said as she sat down for her normal Monday lunch with Inspector Joseph.
Inspector Joseph immediately perked up. "What kind of mystery?"
"Well, it's the strangest thing. But let's start at the beginning."
"As you know, we have three workers in the office, there to handle the mail, billing and bookkeeping. Alice has been there for years and has always been reliable. She has a bit of a drinking problem and a husband who... well, let's just say he has his own problems."
"Barbara is new. She worked in Alaska before coming here, and we're still waiting on her records."
"Our third worker is Clarence. Ever since the new casino boat opened up ... Well, I don't want to point fingers, but there have been some minor irregularities in our petty cash."
"But, here's the mystery. The office is closed all weekend long, every weekend. On Monday mornings, I'm usually the first to arrive. I open up, check the mail, turn off the alarm, etc... I was working the alarm system three weeks back when I noticed the alarm had been shut off on Saturday. For five minutes. Then it got switched back on."
"I thought nothing of it at the time. I just figured someone had forgotten something and had come back to get it."
"But every weekend since, the same thing has happened. The alarm gets shut off on Saturday afternoon for five minutes each time. All three workers have the password and I've asked all three about it. But they've all denied visiting the office."
"As I said, this has been going on for weeks now. Nothing is missing or changed. I've checked the petty cash box and it's always the same as it was on Friday evening. I don't suppose any harm is done, but it's baffling."
"There could be harm," the Inspector cut in. "I can think of one explanation, and I think we need to deal with this right away."
Whom does the inspector suspect, and why?