We have a lilac tree on the patio that grows really well every year. However, last year our neighbour decided to cut the tree back 3 feet + onto our land whilst we were away on holiday and without our permission. He also did this with 2 of our other trees, none of which were over his side of the boundary line. The matter was reported to the police as criminal damage. This year the lilac tree hasn’t grown at all. At the start of the season, one half of the tree started to grow a few leaves, but over the past few weeks they have now died back. We believe there may have been some foul play by the neighbour i.e., weed killer. Is the tree diseased or is it dead? Any advice would be greatly appreciated. I’ve attached an image of the tree as it usually looks each year and 2 of how it looks now.