Testing an Alibi With Travel Time and a Witness
A hardware shop reports a break-in. The shutter was found open at 8:40 p.m. on 3 November and Rs 18,000 in cash was missing. A person of interest, a former employee, states that he was at a community hall function at Chumoukedima from 7:45 p.m. to 9:10 p.m. and never left the hall. The hall is 3.2 km from the shop by road. A witness says the person stepped out at about 8:20 p.m. and returned at about 8:55 p.m. Average walking speed on that stretch is 4 km/h; a two-wheeler averages 24 km/h including parking time. The shop's only CCTV camera faces the road and shows a two-wheeler without a readable number plate passing at 8:30 p.m. Before recording anything in the case diary you must decide what the timeline actually proves.
1. Use the given speeds and distances to assess whether the alibi is broken. Show the calculations.
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Test both travel modes over the 35-minute window the witness describes (8:20 to 8:55 p.m.).
On foot: 3.2 km at 4 km/h = 0.8 hours = 48 minutes each way, so 96 minutes for the round trip. The available window is 35 minutes. A round trip on foot is arithmetically impossible, and even a one-way trip of 48 minutes exceeds the whole window.
By two-wheeler: 3.2 km at 24 km/h = 0.133 hours = 8 minutes each way, so 16 minutes for the round trip, leaving 35 − 16 = 19 minutes at the shop. That is ample for opening a shutter and removing cash.
Conclusion: the statement "I never left the hall" is inconsistent with the witness's account, and the trip is physically possible by two-wheeler but not on foot, while the 8:30 p.m. CCTV sighting is consistent with a vehicle covering this stretch within the window. What this proves is limited, however: it shows the alibi as stated cannot stand if the witness is right. It does not show that the person entered the shop, and it does not identify the two-wheeler. The alibi is broken as a defence, not yet replaced by proof of guilt.
2. The witness's account is the only thing that breaks the alibi. What must you verify before relying on it, and what would you record meanwhile?
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Four things must be verified before the witness is treated as reliable. First, opportunity to observe: where exactly was the witness standing, at what distance, and in what light, since the claimed departure was after dark. Second, precision of timing: "about 8:20" and "about 8:55" are estimates, so I would ask what anchors the times, such as a phone call, a programme item, or an announcement. Third, identification: was the person seen clearly, and can the witness describe clothing that can be checked against the CCTV or the person's own account? Fourth, interest: is there any prior dispute between the witness and the person of interest, which would require corroboration.
On the vehicle side, the CCTV timestamp must be checked against a known clock, since camera drift of even a few minutes matters in a 35-minute window; the passing two-wheeler must be examined frame by frame for a partial plate, a rider's helmet colour, or a delivery box. I would record the calculations, the statement as given in the witness's own words, and the CCTV seizure, while noting expressly that the alibi is unverified rather than false. Any request for call detail records or tower data must go through the lawful written channel, not an informal approach to a service provider.
3. Name one additional fact that would make the alibi collapse decisively, and one that would destroy the witness's version instead.
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A decisive fact against the alibi would be independent proof that the person of interest was on that road during the window: a toll or parking receipt, a fuel slip with a time stamp, or a second camera (shop, bank, fuel station) showing the same two-wheeler with a readable number plate and the rider's clothing matching what he was wearing at the function. The strength of such evidence is that it does not depend on the memory or honesty of the single witness, so it converts a 19-minute window of possibility into a place-and-time fact.
A fact that would destroy the witness's version instead would be proof that the witness was not at the hall at all during that period, or that the person of interest never left: for example, a continuous video of the hall entrance showing him seated throughout, or evidence that the witness had a grudge and had named him falsely. Even then, the case would not be closed; it would simply return to the original position where the alibi stands and other lines of enquiry are needed. The reasoning lesson is that a single uncorroborated witness can open a line of enquiry but cannot be the foundation of a charge, and the case diary should show which of the two possibilities was tested and how.