Reply to the paper details.
According to the paper, Bob should warn the workers before reporting them to the top management. The issue is however complicated considering that the supervisors of the two workers are already aware of the issue. They should have helped to deal with the problem but instead, it seems that they support the two workers considering that they are already friends. The effects of this are that the top management may not trust Bob as they trust the supervisors. The supervisors may also assume the allegations by Bob and this may mean that the two co workers may continue with their activities.
The effects of warning the co workers are that hatred between the co workers and Bob will increase and working with them may be very difficult. The best thing would be to talk with the supervisor first so that the supervisor will feel that the other workers are concerned about the unacceptable acts of the two workers. At this point, it would be easy for the supervisor to talk with the friends so that the problem can be sorted. Warning the workers directly may be not very effective considering that the workers already feel secure under the protection of the supervisor.
The argument that Bob should report the co workers is the best idea. If the management of the organization is concerned about the employees and the security of the people working in the firm, they will take the necessary actions to solve the problem regardless of the person who has reported. The fact that Bob has a supervisor who could have passed the arguments by Bob to the top management wills not hider the management from taking action considering that the issue needs to be addressed the soonest possible for the safety of all people in the working environment including the managers.