The problem with waging a time war was that, no matter what precautions you tried to take, it was hard to guarantee that you'd be able to protect everything you wanted to keep safe. You could set up barriers and temporal shields as much as you wanted, but eventually, some things from either side were going to slip through the cracks.
The crystal that he was tracking at the moment was one such example of unfortunate collateral damage. It had been intended to be a secret weapon, intended to be planted on Dalek-occupied worlds in their relative pasts to give the local population a chance to strike back once they were discovered after the invasion; once they made contact with the crystal, the population could then use the new powers granted to them to confront the Daleks and drive them away, as their new energy-based powers helped them confront the Daleks to a limited degree.
Unfortunately, a few of the TARDISes carrying the crystals had been destroyed by Dalek assault fleets in the Time Vortex before they could reach their destinations, and the crystals had been scattered by their explosion across large areas of time and space. Tracking most of them had been a simple matter of running searches from space for their unique energy signatures, and in cases where they landed on Dalek worlds they ended up fulfilling their original purpose more often than not, but when they landed on populated worlds where the Daleks never emerged…
The consequences varied, but even in a best-case scenario where the crystals augmented a good person, with no obvious enemy for them to face, the presence of such a figure could still be dangerous for the society's social development. On worlds with less technological development, it was fairly easy to find the crystals before they could be triggered, but on more advanced worlds it could be harder to find the crystals from a distance before someone else triggered them by accident, particularly on a planet such as Earth where advanced technology could crop up all over as various aliens left their equipment behind after their defeats.
Actually finding records of the crystal's existence on his favourite planet hadn't been as hard as he'd feared; the challenge lay in finding the right opportunity to eliminate the consequences of its presence without negating his knowledge of it. The Time Vortex might be slightly more 'malleable' with the Time War being waged, but that just made it all the more important that he adhere to the Laws of Time that could still be applied in this situation, and one of them was that he needed to ensure that records remained that would allow him to find the crystal, even if he could limit the damage it caused and make it 'harder' for anyone else to find.
Once he'd found news reports of the devastating battle in Seattle that had unfolded between two of the 'beneficiaries' of the crystal's power, working out where they came from had been a simple matter of identifying the room where the fight had begun and consulting hospital records. After tracking down the name of the person in that room, he'd put together the appropriate equipment before he landed the TARDIS outside the hospital and went inside, making his way directly to the room a few minutes before the 'scheduled' fight was about to begin.
When he saw a man approaching the room who was almost certainly the father of Andrew Detmeer, the man's manner reflecting a petty hostility that the old man rarely encountered, the soldier took the opportunity to act; it might be outside of his self-assigned remit, but no matter how poor a father this man was, he didn't deserve what his son would do to him. As Detmeer senior reached for the door-handle, the old man stepped forward and struck a suitable nerve cluster on his shoulder, leaving the man unconscious and slumped against the wall.
A quick check of the pulse was all he needed to confirm that the other man was alive; his skills with Venusian aikido might be a little rusty given his physical age, but he still had the skull to pull this little trick off. With the father out of the picture for the next few minutes, the old man walked into the room, wincing grimly at the burn damage on the boy's face; it seemed to be mainly cosmetic, but that was still serious.
Unfortunately, as much as he wished he could do more to help this boy, he couldn't simply heal all of his burn damage; eliminating the crystal's influence was one thing, but healing the injuries would attract more attention than he was willing to risk right now. Placing the small box on the boy's chest, he waited for a moment until the device let out a final beep, confirming that it had drained the crystal's energy from him.
It might be too late for him to help this boy's broader mental issues, but he'd prevented him having the 'chance' to hurt any more innocent people; in a situation like this, when the war had to take his full priority, that was the best he could do.
With the other boy who'd been exposed to the crystal dead, the only thing left for him to do here was track down the third 'victim' and take away his own abilities; his response to the crystal's 'gift' might have been more mentally stable, but it was still a very delicate situation that it would be safer to prevent completely.
As with any war, sometimes you had to be satisfied with choosing the best option of a bad bunch…