An old basswood tree that fell and killed a 56-year-old Eden Prairie woman in July was healthy-looking on the outside but decaying and full of insects inside the trunk, police say in a now complete investigation.

Nina Mackay and a friend were walking with her two dogs on a path around Mitchell Lake on July 5 when Mackay was crushed by the falling tree.

Police said in the report that the tree appeared to be close to 100 years old and had a healthy exterior and healthy leaves.

But the inside of the trunk, which was at least 30 inches in diameter, was rotted and full of insects, investigators said.

Mackay’s friend, Fonda Broekhuis of Eden Prairie, told police that she heard a loud cracking sound that sounded like fireworks, then saw a large tree falling toward them.

Other residents heard the sound nearby, describing a loud boom “like fireworks gone bad.” Broekhuis told police she was struck by several branches as the tree fell onto the walking path.

Mackay died from blunt-force injuries, pinned under the trunk of the tree, which had to be removed with a ladder crane.

The two dogs weren’t injured.

Mackay is survived by her husband, 21-year-old son and 18-year-old daughter. They have retained a lawyer to investigate the case.