Here are the correct verb forms for each sentence:

1. The police **have been looking** for a murderer for 2 weeks but they **have not found** him yet.
2. My brother **joined** the army when he was 18.
3. The last time I **went** to London was when I **was** 25. I **did not have** time to visit all the places I **wanted** to.
4. There **have been** great changes in our village in the past few years.
5. He **moved** to Kiev last year where he now **lives**.
6. He **left** for London 2 years ago and I **have not seen** him since then.
7. In the last 6 months I **have completed** 2 English courses.
8. **Have** you **been** to the laboratory this week?