Why don't you call the police? If she says he isn't living there and he IS, it seems like an issue for the police. 

Check your Master Deed or Bylaws to see if there is a clause that enables the HOA to fine the owners in such cases. If not, and your state laws allow, amend the documents to give the authority to the Board to levey fines,and collect them even if they have to foreclose on the unit. 
 

Of course take the owner to court and seek a judgment for her to have her tenant cease and desist. IMO, you should check with an HOA attorney ASAP.

Any act that is illegal, whether harassment or vandalism or whatever, should be reported to the police, even if you don't know who committed the act or have any evidence. Let the police investigate it, which is their job, and they may also determine the place of residence of the boyfriend and see if he has a criminal background. A police presence and investigation is a great deterrent to future problems. I agree with the others who suggest getting better evidence. However, don't wait -- it may be irresponsible to not call the police when crimes are being committed.

I agree the police should be called but only if the BOD knows he is the perpatrator. The police aren't going to spend much time investigating a supposed case of harrassment, vandalism, etc. They have more important crimes to investigate. Only the property owner can have the police remove him from the unit.

How much Police involvement have you had. You need Police intervention/involvement. It sounds like this person has committed some Felony offenses. Suing the unit owner is another matter.

We had a situation similar to yours out our complex. It only takes one unit to bring the value of the whole complex down to almost nothing. Often you will here the landlord say "they are good tenants, they pay their rent on time and don't call for maintenance." To the rest of use they are horrible and make living at the complex misrable. 
 
 
 
I kept calling the police, but nothing seemed to be happening. The response went down racial lines--if a white officer, they politely listened to me, if a black officer, it was all my fault that I had to leave in the dark for work and should mind my own business and not look at the teens being used as "drug mules". I reported the unit was the local "drug hub" numerous times to the police and the board, had pictures of the "drive up service" and prostitution being suppored by this, plus tag numbers of the cars coming in and out. Then, one morning when I was walking to my car and a police officer came out of no where and told me to stop--they had undercover officers in the complex and I was putting myself in danger. Finally, here in Texas we have a judicial process called "Police Abatement" where a judicial order is obtained by the police department to order the landlord to cooperate. Once this happened with both the board and the landlord named in the judgment, the tenants were forced to move if they were not arrested in the final bust. The board was forced to take other measures concerning the people allowed to live in the complex. 
 
 
 
My suggestion is to see if your state has such a statute that allows the police to do this. A Google search will usually answer this for you. Ask to meet with the police officer over the regular patrol officers and go armed with the police abaitment process for your state and all the documentation of the damages, including the landlords refusal to cooperate. Often the police are not able to enter the property as it is private property unless they have a call or "probable cause". The police should be able to give you some ideas of how to work with them and now that the "boss" is aware, he/she will follow up with the regular patrol officers to be more on the lookout for problems.

I wouldn't waste time trying to get cooperation from the renters. Your legal relationship is with the homeowner. Everytime a violation occurs send a letter to the homeowner and start the fining process (depending on how your rules are structured). If the homeowner doesn't pay the fines then put a lien against the condo. If that still doesn't work turn the owner over to an attorney. Let the homeowner take the burden of resolving the the idiot doing the harm. Remember, the owner is a landlord making money off of rental income. He should do the behavior control of the tenant, not the board. Certainly if you do catch him in a violation that is actually illegal then call the police immediately. You must have rules that assure "quiet enjoyment of each unit". If the neighbors are complaining about noise or vandalism issues then there should be rules to protect the community. You have my sympathy!

Check your governing docs for procedures to make an assessment chargeable to this condo owner for expenses caused by this situation. For example, if the association paid to fix damage attributable to this condo, then assess the cost to the condo. (This is not a fine, but is more like a reimbursement.) See if a bill gets the owner's attention.

Board should make up a rental agreement with all the rules and regulation that as a renter they must follow. Have the renters sign it after approval by the board of the new renters, and before the renters are allowed to move in. The association would then have it all in writing and all would understand the do's and don'ts's. All will get a better understanding and documented of it all should the police or courts get involved. Maybe you can put in clauses where any visitor that stays with someone say more then 2 weeks or a month must get board approval to stay any longer.