Looking on the internet deeply has found these results:

Dont mourn at the dead is the most popular phrase on the web.

Dont mourn on the dead 1674,000 results on the web	Dont mourn at the dead 1810,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Luisa believed that the dead kept being present. The dead can return given sufficient motivation. Romero never explained why the dead rise. In Florence painters dissect the dead. They thought she could speak to the dead. People always remember the dead fondly. Unless you can raise the dead... The dead are the cornerstone of every homicide investigation.	The dead are the cornerstone of every homicide investigation. The dead can return given sufficient motivation. People always remember the dead fondly. They thought she could speak to the dead. Luisa believed that the dead kept being present. Supports the decision of President Boris Tadic to go to mourn at the Potocari memorial on the tenth anniversary of the Srebrenica massacre; In Florence painters dissect the dead. Unless you can raise the dead...

Dont mourn on the dead

1674,000 results on the web

Dont mourn at the dead

1810,000 results on the web

More popular!

The dead are the cornerstone of every homicide investigation.
The dead can return given sufficient motivation.
People always remember the dead fondly.
They thought she could speak to the dead.
Luisa believed that the dead kept being present.
Supports the decision of President Boris Tadic to go to mourn at the Potocari memorial on the tenth anniversary of the Srebrenica massacre;
In Florence painters dissect the dead.
Unless you can raise the dead...