The truth, the whole truth and nothing but the truth.
I'll use an example from my working life to illustrate what I mean.
Two guys I worked in an office with got in a physical altercation. A lot of us where in the same open plan office at the time. Lots of corners, partitions, white boards etc used to break up the space though, so no-one had a clear view of the whole situation.
We were interviewed about this and had to sign our statement.
The truth- I heard a noise, looked up and saw J and G physically fighting.
The whole truth- I had seen resentment simmer between the two for a while now. Lots of verbal confrontations and practical "jokes" designed to cause embarrassment/discomfort.
I had also recently witnessed J use G's disability (deafness) against him- mock G behind his back when he couldn't lip read, turn up a radio loud to cause feedback on G's hearing aid and I had both challenged J in this and spoken to B (J and G's manager) about it.
I had heard from B the previous day that there had been a big verbal confrontation between J and G whilst I was out of the office. B had chosen to speak to me about it as the senior manager was out of the office all week on a training course. I was on the same level as B in a different branch of the org chart, so we were both the most senior in absence of the overall manager. The disagreement was over a seating reorganization- J and G both wanted to sit in the same seat. J came in at 5am on the morning of the reorganization to "bag" the preferred seat, even though the team and management decision had been that that seat should remain empty (as J and G couldn't decide between themselves about it, it had been obviously causing resentment and there was a need for a "spare" desk for visitors from another office). So B and I decided to enforce that decision, with the addition of separating J and G as far away from one another as operationally possible. This designed to be a temporary thing. We emailed the senior manager and HR about it saying this was our temporary solution, but the situation needed to be better addressed on the manager's return. HR and manager both fine with this.
The next day, J kept going up behind G and tapping him on the shoulder to startle him- both B and I had told G to stop doing this and made it clear that it was unacceptable to harrass a disabled person on the basis of the disability. He was told if he did it again he would be sent home immediately. HR were consulted and said they were happy with that.
Later I saw G walk past my desk carrying a glass of iced water. A few moments later I heard a yell, looked up and saw basically a fist fight.
Nothing but the truth- I had my back to the incident and had to turn round to witness it after I heard the noise. As a result I have no idea who threw the first punch.
To be honest, I'd be very surprised if it wasn't G who threw the first punch. J admitted walking up behind him and tipped a glass of iced water over G.
But I didn't see G throw a punch, and to be honest, even if he did, I thought J had physically assaulted him first and scared him out of his skin to the extent it wasn't fair to expect hI'm to know he wasn't under attack. So I kept all my opinions to myself.
Both were suspended during the investigation. After the investigation, a workplace audit was conducted to see if we could better meet G's additional workplace needs. The upshot of that was that our employer contributed to upgrading his hearing aid to one that was with background noise and which had less whiny feedback (he had to switch off his old one a lot as a result of the latter, and it was recognised that this was hugely unfair to him to have to give up his hearing like that). A workplace champion was also appointed to G outside his line management structure (it was me). So I sat in on a lot of meetings with him, went to see occupational health with him whilst he was choosing a new hearing aid etc. J wasn't sacked- there wasn't enough conclusive evidence from all the witness statements to do that. But he was on a temporary contract and it wasn't renewed when it was finished (about 6 weeks later).
Unsurprisingly, G was pretty shaken/upset by the whole thing. We used to go for a coffee after his occupational health/audiology appointments and we spoke about it a lot. He decided he was underemployed in his office role and decided to retrain. Whilst he was getting a new hearing aid, he got really interested in the different types of hearing aid. He also met a deaf audiologist and a light went on- he'd be really good at being an audiologist because he understood what it's like to be deaf. So he decided to retrain as an audiologist in the NHS. He asked me to help him with his application outside work, so I did, on the hush hush. I left around the same time to take up a role elsewhere, as I thought the situation should have been handled better earlier.