Sometimes the best way to deal with an uncooperative witness is to expect them to be uncooperative ahead of time and be prepared for that. You should prepare clean, tight questions which offer as little opportunity as possible for evasive responses. When uncooperative witnesses respond with “I don’t know,” you can try to convince them that while they might not know, there is a plausible standard, definition or explanation which they can accept as truth. When uncooperative witnesses try to stall by saying they don’t understand a question, you can exhaust all of their reasons for supposedly not understanding the question, then re-phrase the question. You can also parse the sentence in order to get them to admit things little by little. When uncooperative witnesses say they don’t remember facts relating to numbers, such as dates or times, you can get them to commit to the smallest and largest possible values then close the gap. So, if a witness says they don’t remember how long it takes to get from one place to another, you could get them to agree that it couldn’t take longer than 50 minutes and couldn’t take longer than 20 minutes, then close that gap from there.