Editing digital files always leaves fingerprints. Video is compressed, and to edit it, it has to be uncompressed, altered, and recompressed. A competent computer forensic expert should be able to testify that the video is as shot by the camera.
The encoding done by the h.264 encoding chip in the camera may have specific characteristics that do not match the compression done by the editing software.
This is why I suggest keeping the original file. Even just trimming the video down usually involved uncompress/alter/recompress and you lose that fingerprint of the original encoding.
In most cases, it would not be worth hiring a forensic expert, but in some cases it might, and in any case as digger pointed out, handing over the SD card as evidence within a short time after the incident would be a significant argument.
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