Who killed Melvin Tuttle?

Hint 1 of 8:

Tuttle gave his girlfriend some information on some seedy business deals.

Hint 2 of 8:

Both Swathmore and Livingston were searching through his locker at Bell's
Baths to find that information.

Hint 3 of 8:

If you talked to H. R. Murray, you should know that Tuttle was poisoned.

Hint 4 of 8:

And if you did any research at the library, you should know about the poison
that killed Tuttle.

Hint 5 of 8:

Chinaberry smells like lilac.

Hint 6 of 8:

Heathcliff received an envelope scented like lilac.