To whom did the bifocals belong to in the movie Chinatown?

Question

In the 1974 movie Chinatown the following happens:

At Evelyn's mansion, Gittes finds her servants packing her things. He realizes her garden pond is salt water and discovers a pair of bifocals in it. He confronts Evelyn about her "sister"; after Gittes slaps her, she admits that the woman, Katherine, is her sister and her daughter: her father raped her when she was fifteen. She says that the eyeglasses are not Mulwray's, as he did not wear bifocals. Wikipedia-Chinatown

As the bifocals were not belonging to Mulwray, why did Gittes accuse Cross of murdering Mulwray in the salt water and leaving the bifocals in the pond?

Answer 1

Gittes concludes that they're Noah Cross's. From the script:

GITTES: An obituary column... can you read in this light?

CROSS: Yes... I think I can manage...

Cross dips into his coat pocket and pulls out a pair of rimless glasses.. He puts them on, reads. Gittes stares at the bifocal lenses as Cross continues to look through the obituary column. He looks up.

CROSS: What does this mean?

GITTES: -- that you killed Hollis Mulwray --

Gittes is holding the bifocals with the broken lens now.

GITTES: (continuing) -- right here, in this pond. You drowned him... and you left these.

And since Noah takes them away from him as to not incriminate himself, Gittes is probably right.