All events ultimately depend on God’s Providential decisions.
A demon can kill a human being if God allows the demon to do so. A demon can rarely do so however, directly or physically – that would be an especial loosening of the restrictions God places on demons normally. These restrictions are quite great, preventing a great deal of disaster.
God also restrains his good angels from intervening as greatly as they could. One always has a guardian angel at one’s side. And these angels of course have the Lord and they constantly protect us – the degree they are permitted to do so depends on the Lord’s will.
The spirits are en mass restrained to a degree from intervening in our lives however, both angels and devils from exercising their full abilities, which are tremendous.
The demon works through mediation – i.e., he (rarely) possesses or (normally) offers the temptation to a human being. So it is simple for a demon to offer the temptation for one human being to kill another human being, or for that human being to kill himself.
The demons in fact favor murder-suicides, when you read about these events in the newspapers you often read about that same person talking about demons (which are in the secular papers always ascribed to mental illnesses). Drugs-murder-rape-suicide these are the baliwick of devils.
For example while you are driving on the highway the demon could have tempted an alcoholic to drink to much, and then try to tempt him to swerve the car into yours – or he could try to tempt you personally to turn the wrong way off a cliff’s edge, or similar.
However at the same time all this is happening God and the angels involved are offering the good choice to those involved.
The demons are often more directly persuasive on these matters because they do not care about the human freedom of the person being persuaded in the slightest.
Whether you will be harmed or not by a devil depends on the interaction between sin and Providence in the particular situation.
Generally the best method for a safe and protected life with beneficial Providential interaction and minimum sinful interaction is to be as holy and saintly as possible.
Even the worst of sinners who suddenly turns to the Lord in the darkest situation is in good hands.
But do avoid them lest you reap what you sow.
‘Above all we ought at least to know that there are three origins of our thoughts, i.e., from God, from the devil, and from ourselves. . . We ought then carefully to notice this threefold order, and with a wise discretion to analyse the thoughts which arise in our hearts, tracking out their origin and cause and author in the first instance, that we may be able to consider how we ought to yield ourselves to them. . .’
St. Moses the Black Hermit
