The weapon (@Chrone got it):
Welcome mat, Ché Guevarra --> Bienvenu chez (french). The initial 'w' of welcome is cut off?
More likely what @Chrone said: Ché in a mat --> machet(e), the final 'e' is missing.
Looks like 'dar es-salaam' (arabic) but mirror image, and in pieces. Broken mirror? Also the final 'm' is missing.
The victim (@OmegaKrypton's hint)
Looks like a periodic table: aha! The columns are element names. Arsenic Holmium Silicon Hassium Caesium Tantalum Tellurium.
The fourth letter of each If you spelled them vertically from the top then the letters in red spell EMISSAR(Y), final 'y' is missing.
The time: see @BladeWraith's hint and @olim's answer
If I got the final answer right (see below), the missing letter is an R, and OP says "time of year", then I guess
SUMMER, so the word to fill in is --S-U--M-M-E- ??? HAS CUTE MOMENT ??? Oh wait, WINTER works too, duh... --W-I--N-T-E- ??? DOWN IN ANOTHER ??? (random guesses) nope, wayyy off :-) As @olim explains, it's DECEMBE(R). The missing letter is indeed R.
The missing letters are _EMY, well if he's french, then probably RÉMY.