The Car Gas Tank Mystery

Well, things started about 3 weeks ago when my son was in a wreck in our Toyota Tacoma. My husband thought he would drive into Springfield to see what he could do to help my son, only to discover that there was no gas in the Jeep Cherokee. We never drive that vehicle as we haven't got it legal to drive yet but we thought that it had about a quarter of a tank of gas in it. I tried to think about it and thought maybe with us using it occasionally to take trash down to the dumpster that we had ran it out and hadn't realized it. We didn't give it another thought until we went to get new tires on the Tacoma. The tires we replaced on it were bigger than the ones that were on it before so we thought maybe it was affecting our gas mileage. We continued to watch it and then got to thinking that maybe our son was not putting all the money that we gave him for gas into the vehicle or that he was driving more than what he said that he was. We continued to watch and the problem persisted so we sent our daughter with him on one occasion. The truck had a quarter of a tank of gas in it when he left and when my husband got up the next morning to head to work the gas light was on. We questioned our daughter about it the next day and she said that our son went exactly where we had sent them. A few days later we went to return my mother-in-law's vehicle to her and drove forever on a quarter of a tank of gas. It was then that we decided our neighbor had to be the one that was stealing it. You might ask how we came to this conclusion. We came to this conclusion as we have not had a neighbor for the past 6 months and have had no problems at all. The new neighbor that has moved next door is an ex-military guy who has a knocked up girlfriend that is not working. He has a couple of girls from a previous marriage and works as a semi-truck mechanic at a local trucking company. He claims he only makes $170/week, got his truck repossessed the other day and says that his car is not far behind. He claims to have mental issues and I think that he probably does. My guess is that he probably can't afford the gas and definitely most likely has all the tools he needs to siphon gas easily and quickly. I will now be buying a locked gas cap and hope that this resolves the conflict without any confrontation on either party's part. If this doesn't solve the problem then I guess I will have to pull the video camera out and see what I can catch on video :)
This is my first entry and first time blogging so please be kind if you read :)